The ball screw shaft used in a lead screw mechanism is provided with a mounting shaft portion having no screw thread formed thereon at one end thereof for mounting a bearing member or a drive gear thereon.
The mounting shaft portion is typically integrally formed with the ball screw shaft, and it was necessary to use a special machine tool and a jig for machining the mounting shaft portion. Even when the thread of the ball screw shaft is the same, the configuration of the mounting shaft portion may vary depending on the need of the user. Similarly, even when the configuration of the mounting shaft portion is the same, the length of the threaded shaft may vary. Such variations inevitably created bottlenecks in the manufacturing process. Furthermore, the threaded shaft portion is quenched along with the mounting shaft portion, but the mounting shaft portion is required to be annealed because the quenched member cannot be easily machined.
In connection with such a ball screw shaft, it is known to manufacture the mounting shaft portion (shaft end adapter) and the screw shaft portion as separate component parts, and integrally join the two parts by brazing, welding or shrink fitting. See Patent Documents 1 and 2.